Piezoelectric actuator, time piece, and portable device

ABSTRACT

A rectangular vibrating plate  10  in which a piezoelectric element and a reinforcing plate are stacked is supported on a main plate by a support member  11 , and is urged toward the rotor  100  by an elastic force of the support member  11 . This brings a projection  36  provided on the vibrating plate  10  into abutment with an outer peripheral surface of the rotor  100 . In this construction, when the vibrating plate  10  vibrates in the horizontal direction in the figure by an applied voltage from a driving circuit (not shown), the rotor  100  is rotated in a clockwise direction in accordance with the displacement of the projection  36  due to the vibration.

TECHNICAL FIELD

The present invention relates to a piezoelectric actuator, and to atimepiece and a portable device including the piezoelectric actuator.

BACKGROUND ART

Since piezoelectric elements have excellent responsiveness andconversion efficiency from electrical energy to mechanical energy,various types of piezoelectric actuators utilizing the piezoelectriceffect of piezoelectric elements have been developed in recent years.The piezoelectric actuators have been applied to the fields ofpiezoelectric buzzers, ink-jet heads of printers, and ultrasonic motors.

FIG. 61 is a plan view schematically showing an ultrasonic motor using aconventional piezoelectric actuator. As shown in the figure, theultrasonic motor of this type is called a poking type in which a rotorsurface is slightly inclined and brought into contact with a tip of avibrating piece connected to a piezoelectric element. In such aconstruction, when the piezoelectric element is expanded and contractedby an alternating voltage from an oscillator, and the vibrating piecereciprocates in a longitudinal direction, a force component is generatedin a circumferential direction of the rotor and the rotor is rotated.

In addition, a technique has been known in which two ultrasonicvibrators (piezoelectric elements) are included, the ultrasonicvibrators vibrate with their own electrical resonance frequencies, and avibrating piece is displaced by the vibration (Japanese UnexaminedApplication Publication No. 10-25151).

However, while the displacement of the piezoelectric element depends onthe applied voltage, it is very small, usually about sub-micron, andthis also applies to a case where the piezoelectric element vibrateswith the above-described resonance frequency. For this reason, thedisplacement is amplified by a certain amplification mechanism, and istransmitted to the rotor. When the amplification mechanism is used,however, energy is consumed to operate the amplification mechanism,efficiency is lowered, and the size of an apparatus increases. Inaddition, when the amplification mechanism is used, it may be difficultto stably transmit a driving force to the rotor.

In addition, since a small portable device, such as a wristwatch, isdriven by a battery, it is necessary to lower the consumption ofelectronical energy and the drive voltage. Therefore, when apiezoelectric actuator is incorporated into such a portable device, itis particularly required that the energy efficiency be high and thedrive voltage be low.

Incidentally, in a calendar display mechanism for displaying the date,the day, and so forth in a timepiece or the like, it is common for therotational driving force from an electromagnetic stepping motor to beintermittently transmitted to a date indicator or the like via awatch-hand-driving wheel train so as to advance the date indicator orthe like. On the other hand, since the wristwatch is carried by beingstrapped on a wrist, a reduction in thickness for convenience ofcarrying has long been demanded. In order to pursue the reduction inthickness, it is also necessary to reduce the thickness of the calendardisplay mechanism. However, since the stepping motor is constructed byincorporating parts, such as a coil and a rotor, thereinto in anout-of-plane direction, the reduction in thickness of the calendardisplay mechanism is limited. For this reason, there is a problem inthat the conventional calendar mechanism using the stepping motor is notstructurally suited for reducing the thickness.

In particular, in order to share a mechanical system (a so-calledmovement) between a timepiece with a calendar display mechanism and atimepiece without such a display mechanism, it is necessary to constructthe calendar display mechanism on the side of a dial. However, it isdifficult for an electromagnetic stepping motor to achieve a reductionin thickness to such an extent that the calendar mechanism can beconstructed on the side of the dial. Therefore, it is necessary for aconventional timepiece to be manufactured by separately designingwatch-hand-driving mechanical systems according to whether there is adisplay mechanism, and this becomes a problem when improving theproductivity thereof.

The present invention is made in consideration of the foregoingcircumstances, and an object is to provide a piezoelectric actuator thatfacilitates a reduction in size by simplifying conductive construction,and to provide a timepiece and a portable device including the same. Inaddition, it is an object to provide a piezoelectric actuator that isable to efficiently transmit vibrations of a piezoelectric element, thatis suited for a reduction in size and thickness, and that is able tostably transmit a driving force, and to provide a timepiece and aportable device including the same.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a piezoelectricactuator comprising: a base frame; a vibrating plate in which alongitudinal plate-like piezoelectric element and a reinforcing portionare stacked; and a support member, which is an elastic member, having afixing portion fixed to the base frame and a mounting portion mounted onthe vibrating plate, and which provides an elastic force to thevibrating plate so that a longitudinal end of the vibrating plate abutsagainst an object to be driven; wherein, when the piezoelectric elementvibrates in the longitudinal direction of the vibrating plate, thevibrating plate is vibrated by the vibration, and the object to bedriven is driven in one direction in accordance with the displacement ofthe vibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a support member having a fixing portion fixed tothe base frame and a mounting portion mounted on the vibrating plate,and supporting the vibrating plate on the base frame; and an elasticmember for providing an elastic force to the vibrating plate so that thelongitudinal end of the vibrating plate abuts against an object to bedriven; wherein, when the piezoelectric element vibrates in thelongitudinal direction of the vibrating plate, the vibrating plate isvibrated by the vibration, and the object to be driven is driven in onedirection in accordance with the displacement of the vibrating plate dueto the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having front and back surfaces, androtationally supported on the base frame in the direction perpendicularto the front and back surfaces as the direction of a rotation axis; anda support member, which is an elastic member, having a fixing portionfixed to the base frame and a mounting portion mounted on the vibratingplate, and which provides an elastic force to the vibrating plate sothat a longitudinal end of the vibrating plate abuts against the frontsurface or the back surface of the rotor; wherein, when thepiezoelectric element vibrates in the longitudinal direction of thevibrating plate, the vibrating plate is vibrated by the vibration, andthe rotor is driven in one direction in accordance with the displacementof the vibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having front and back surfaces, androtationally supported on the base frame in the direction perpendicularto the front and back surfaces as the direction of a rotation axis; asupport member having a fixing portion fixed to the base frame and amounting portion mounted on the vibrating plate, and supporting thevibrating plate on the base frame; and an elastic member for providingan elastic force to the vibrating plate so that the longitudinal end ofthe vibrating plate abuts against the front surface or the back surfaceof the rotor; wherein, when the piezoelectric element vibrates in thelongitudinal direction of the vibrating plate, the vibrating plate isvibrated by the vibration, and the rotor is driven in one direction inaccordance with the displacement of the vibrating plate due to thevibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface, androtationally supported on the base frame; and a support member, which isan elastic member, having a fixing portion fixed to the base frame and amounting portion mounted on the vibrating plate, and which provides anelastic force to the vibrating plate so that a longitudinal end of thevibrating plate abuts against the outer peripheral surface of the rotor;wherein, when the piezoelectric element vibrates in the longitudinaldirection of the vibrating plate, the vibrating plate is vibrated by thevibration, and the rotor is driven in one direction in accordance withthe displacement of the vibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface, androtationally supported on the base frame; a support member having afixing portion fixed to the base frame and a mounting portion mounted onthe vibrating plate, and supporting the vibrating plate on the baseframe; and an elastic member for providing an elastic force to thevibrating plate so that the longitudinal end of the vibrating plateabuts against the outer peripheral surface of the rotor; wherein, whenthe piezoelectric element vibrates in the longitudinal direction of thevibrating plate, the vibrating plate is vibrated by the vibration, andthe rotor is driven in one direction in accordance with the displacementof the vibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface,rotationally supported on the base frame, a rotating shaft thereof beingmovable; a support member having a fixing portion fixed to the baseframe and a mounting portion mounted on the vibrating plate, andsupporting the vibrating plate on the base frame; and an elastic memberfor providing an elastic force to the rotor so that the outer peripheralsurface of the rotor abuts against the longitudinal end of the vibratingplate; wherein, when the piezoelectric element vibrates in thelongitudinal direction of the vibrating plate, the vibrating plate isvibrated by the vibration, and the rotor is driven in one direction inaccordance with the displacement of the vibrating plate due to thevibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface, androtationally supported on the base frame; and a support member having afixing portion fixed to the base frame and a mounting portion mounted onthe vibrating plate, and supporting the vibrating plate on the baseframe; wherein the rotor is formed of an elastic body arranged on aposition where the outer peripheral surface thereof abuts against thelongitudinal end of the vibrating plate, and presses the outerperipheral surface against the end of the vibrating plate by the elasticforce thereof; and wherein, when the piezoelectric element vibrates inthe longitudinal direction of the vibrating plate, the vibrating plateis vibrated by the vibration, and the rotor is driven in one directionin accordance with the displacement of the vibrating plate due to thevibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a selection means for selecting either alongitudinal vibration for vibrating the vibrating plate in thelongitudinal direction within a plane to which the vibrating platebelongs, or a bending vibration for vibrating the vibrating plate in thewidthwise direction perpendicular to the longitudinal direction withinthe plane; and a support member, which is an elastic member, having afixing portion fixed to the base frame and a mounting portion mounted onthe vibrating plate, and which provides an elastic force to thevibrating plate so that a longitudinal end of the vibrating plate abutsagainst an object to be driven; wherein, when the longitudinal vibrationis selected by the selection means, the vibrating plate causes thelongitudinal vibration, whereby the object to be driven is driven in onedirection in accordance with the displacement of the vibrating plate dueto the vibration, and wherein, when the bending vibration is selected bythe selection means, the vibrating plate causes the bending vibration,whereby the object to be driven is driven in the direction opposite tothe direction during the longitudinal vibration in accordance with thedisplacement of the vibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a selection means for selecting either alongitudinal vibration for vibrating the vibrating plate in thelongitudinal direction within a plane to which the vibrating platebelongs, or a bending vibration for vibrating the vibrating plate in thewidthwise direction perpendicular to the longitudinal direction withinthe plane; a support member having a fixing portion fixed to the baseframe and mounting portion mounted on the vibrating plate, andsupporting the vibrating plate on the base frame; and an elastic memberfor providing an elastic force to the vibrating plate so that alongitudinal end of the vibrating plate abuts against an object to bedriven; wherein, when the longitudinal vibration is selected by theselection means, the vibrating plate causes the longitudinal vibration,whereby the object to be driven is driven in one direction in accordancewith the displacement of the vibrating plate due to the vibration, andwherein, when the bending vibration is selected by the selection means,the vibrating plate causes the bending vibration, whereby the object tobe driven is driven in the direction opposite to the direction duringthe longitudinal vibration in accordance with the displacement of thevibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having front and back surfaces, androtationally supported on the base frame in the direction perpendicularto the front and back surfaces as the direction of a rotation axis; aselection means for selecting either a longitudinal vibration forvibrating the vibrating plate in the longitudinal direction within aplane to which the vibrating plate belongs, or a bending vibration forvibrating the vibrating plate in the out-of-plane direction; and asupport member, which is an elastic member, having a fixing portionfixed to the base frame and a mounting portion mounted on the vibratingplate, and which provides an elastic force to the vibrating plate sothat a longitudinal end of the vibrating plate abuts against the frontsurface or the back surface of the rotor; wherein, when the longitudinalvibration is selected by the selection means, the vibrating plate causesthe longitudinal vibration, whereby the rotor is rotationally driven inone direction in accordance with the displacement of the vibrating platedue to the vibration, and wherein, when the bending vibration isselected by the selection means, the vibrating plate causes the bendingvibration, whereby the rotor is rotationally driven in the directionopposite to the direction during the longitudinal vibration inaccordance with the displacement of the vibrating plate due to thevibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having front and back surfaces, androtationally supported on the base frame in the direction perpendicularto the front and back surfaces as the direction of a rotation axis; aselection means for selecting either a longitudinal vibration forvibrating the vibrating plate in the longitudinal direction within aplane to which the vibrating plate belongs, or a bending vibration forvibrating the vibrating plate in the out-of-plane direction; a supportmember having a fixing portion fixed to the base frame and a mountingportion mounted on the vibrating plate, and supporting the vibratingplate on the base frame; and an elastic member for providing an elasticforce to the vibrating plate so that a longitudinal end of the vibratingplate abuts against the front surface or the back surface of the rotor;wherein, when the longitudinal vibration is selected by the selectionmeans, the vibrating plate causes the longitudinal vibration, wherebythe rotor is rotationally driven in one direction in accordance with thedisplacement of the vibrating plate due to the vibration, and wherein,when the bending vibration is selected by the selection means, thevibrating plate causes the bending vibration, whereby the rotor isrotationally driven in the direction opposite to the direction duringthe longitudinal vibration in accordance with the displacement of thevibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface, androtationally supported on the base frame; a selection means forselecting either a longitudinal vibration for vibrating the vibratingplate in the longitudinal direction within a plane to which thevibrating plate belongs, or a bending vibration for vibrating thevibrating plate in the widthwise direction perpendicular to thelongitudinal direction within the plane; and a support member, which isan elastic member having a fixing portion fixed to the base frame and amounting portion mounted on the vibrating plate, and which provides anelastic force to the vibrating plate so that a longitudinal end of thevibrating plate abuts against the outer peripheral surface of the rotor;wherein, when the longitudinal vibration is selected by the selectionmeans, the vibrating plate causes the longitudinal vibration, wherebythe rotor is rotationally driven in one direction in accordance with thedisplacement of the vibrating plate due to the vibration, and wherein,when the bending vibration is selected by the selection means, thevibrating plate causes the bending vibration, whereby the rotor isrotationally driven in the direction opposite to the direction duringthe longitudinal vibration in accordance with the displacement of thevibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface, androtationally supported on the base frame; a selection means forselecting either a longitudinal vibration for vibrating the vibratingplate in the longitudinal direction within a plane to which thevibrating plate belongs, or a bending vibration for vibrating thevibrating plate in the widthwise direction perpendicular to thelongitudinal direction within the plane; a support member having afixing portion fixed to the base frame and a mounting portion mounted onthe vibrating plate, and supporting the vibrating plate on the baseframe; and an elastic member for providing an elastic force to thevibrating plate so that a longitudinal end of the vibrating plate abutsagainst the outer peripheral surface of the rotor; wherein, when thelongitudinal vibration is selected by the selection means, the vibratingplate causes the longitudinal vibration, whereby the rotor isrotationally driven in one direction in accordance with the displacementof the vibrating plate due to the vibration, and wherein, when thebending vibration is selected by the selection means, the vibratingplate causes the bending vibration, whereby the rotor is rotationallydriven in the direction opposite to the direction during thelongitudinal vibration in accordance with the displacement of thevibrating plate due to the vibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface,rotationally supported on the base frame, a rotating shaft thereof beingmovable; a selection means for selecting either a longitudinal vibrationfor vibrating the vibrating plate in the longitudinal direction within aplane to which the vibrating plate belongs, or a bending vibration forvibrating the vibrating plate in the widthwise direction perpendicularto the longitudinal direction within the plane; a support member havinga fixing portion fixed to the base frame and a mounting portion mountedon the vibrating plate, and supporting the vibrating plate on the baseframe; and an elastic member for providing an elastic force to the rotorso that the outer peripheral surface of the rotor abuts against alongitudinal end of the vibrating plate; wherein, when the longitudinalvibration is selected by the selection means, the vibrating plate causesthe longitudinal vibration, whereby the rotor is rotationally driven inone direction in accordance with the displacement of the vibrating platedue to the vibration, and wherein, when the bending vibration isselected by the selection means, the vibrating plate causes the bendingvibration, whereby the rotor is rotationally driven in the directionopposite to the direction during the longitudinal vibration inaccordance with the displacement of the vibrating plate due to thevibration.

In another form of the present invention, there is provided apiezoelectric actuator comprising: a base frame; a vibrating plate inwhich a longitudinal plate-like piezoelectric element and a reinforcingportion are stacked; a rotor having an outer peripheral surface, androtationally supported on the base frame; a selection means forselecting either a longitudinal vibration for vibrating the vibratingplate in the longitudinal direction within a plane to which thevibrating plate belongs, or a bending vibration for vibrating thevibrating plate in the widthwise direction perpendicular to thelongitudinal direction within the plane; and a support member having afixing portion fixed to the base frame and a mounting portion mounted onthe vibrating plate, and supporting the vibrating plate on the baseframe; wherein the rotor is formed of an elastic body arranged on theposition where the outer peripheral surface thereof abuts against alongitudinal end of the vibrating plate, and presses the outerperipheral surface against the end of the vibrating plate by the elasticforce thereof; wherein, when the longitudinal vibration is selected bythe selection means, the vibrating plate causes the longitudinalvibration, whereby the rotor is rotationally driven in one direction inaccordance with the displacement of the vibrating plate due to thevibration, and wherein, when the bending vibration is selected by theselection means, the vibrating plate causes the bending vibration,whereby the rotor is rotationally driven in the direction opposite tothe direction during the longitudinal vibration in accordance with thedisplacement of the vibrating plate due to the vibration.

From another standpoint, according to the present invention, there isprovided a piezoelectric actuator having a piezoelectric element, anddriving an object to be driven by the vibration of the piezoelectricelement; the piezoelectric actuator comprising reinforcing portionsstacked on the upper and lower sides of the piezoelectric element;wherein power is supplied to the piezoelectric element via thereinforcing portions.

In another form of the present invention, there is provided apiezoelectric actuator having a piezoelectric element, and driving anobject to be driven by the vibration of the piezoelectric element; thepiezoelectric actuator comprising: a base frame; and a support memberformed of a conductive material, and supporting the piezoelectricelement on the base frame; wherein power is supplied to thepiezoelectric element via the support member.

In another form of the present invention, there is provided apiezoelectric actuator having a piezoelectric element, and driving anobject to be driven by the vibration of the piezoelectric element; thepiezoelectric actuator comprising an elastic conductive materialcontacting the upper and lower surfaces of the vibrating plate to clampthe vibrating plate; wherein power is supplied to the piezoelectricelement via the elastic conductive material.

In another form of the present invention, there is provided apiezoelectric actuator having a piezoelectric element, and driving anobject to be driven by the vibration of the piezoelectric element; thepiezoelectric actuator comprising a wire wound around the vibratingplate while being in contact therewith; wherein power is supplied to thepiezoelectric element via the wire.

In addition, according to the present invention, there is provided atimepiece comprising: a piezoelectric actuator in any one of the aboveforms; and a ring-shaped calendar display wheel rotationally driven bythe piezoelectric actuator.

Furthermore, according to the present invention, there is provided aportable device comprising: a piezoelectric actuator in any one of theabove forms; and a battery for supplying power to the piezoelectricactuator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the principal construction of a calendardisplay mechanism having a piezoelectric actuator incorporated thereinin a timepiece according to a first embodiment of the present invention.

FIG. 2 is a sectional side elevation schematically showing theconstruction of the timepiece according to the embodiment.

FIG. 3 is a plan view showing the overall construction of thepiezoelectric actuator.

FIG. 4 includes diagrams for explaining a sectional contact statebetween a rotor and a projection that are components of thepiezoelectric actuator.

FIG. 5 is a diagram for explaining another example of the sectionalcontact state between the rotor and the projection of the piezoelectricactuator.

FIG. 6 is a sectional side elevation showing a vibrating plate that is acomponent of the piezoelectric actuator.

FIG. 7 is a diagram showing a state in which the vibrating plate causesa longitudinal vibration.

FIG. 8 is a block diagram showing the outline of the construction forsupplying electric power to a piezoelectric element of the vibratingplate.

FIG. 9. is a block diagram showing the outline of another constructionfor supplying electric power to the piezoelectric element of thevibrating plate.

FIG. 10 is a diagram for explaining a state in which, when the vibratingplate vibrates, it causes a bending vibration by a reaction force fromthe rotor.

FIG. 11 is a diagram for explaining the orbit of the projection duringthe bending vibration.

FIG. 12 is a graph showing an example of the relationship betweenvibration frequency and impedance of the vibrating plate.

FIG. 13 is a diagram for explaining the amplitude of the vibrating plateduring the bending vibration.

FIG. 14 is a diagram for explaining the operation of the vibrating platewhen the rotor is to be rotated in a reverse direction.

FIG. 15 is a diagram for explaining the position of the center ofrotation of a support member for rotationally supporting the vibratingplate.

FIG. 16 is a diagram for explaining another example of the position ofthe center of rotation of the support member for rotationally supportingthe vibrating plate.

FIG. 17 is a sectional side elevation showing a principal constructionof the calendar display mechanism.

FIG. 18 is a block diagram showing the construction of a driving circuitof the calendar display mechanism.

FIG. 19 is a timing chart showing the operation of the driving circuit.

FIG. 20 is a plan view showing a first modification of the piezoelectricactuator.

FIG. 21 is a sectional side elevation of a vibrating plate of a secondmodification of the piezoelectric actuator.

FIG. 22 is a plan view showing another example of the vibrating plate ofthe second modification of the piezoelectric actuator.

FIG. 23 is a plan view showing a third modification of the piezoelectricactuator.

FIG. 24 is a plan view showing another example of a vibrating plate ofthe third modification of the piezoelectric actuator.

FIG. 25 is a plan view showing still another example of the vibratingplate of the third modification of the piezoelectric actuator.

FIG. 26 is a diagram showing a further example of the vibrating plate ofthe third modification of the piezoelectric actuator.

FIG. 27 is a diagram showing a still further example of the vibratingplate of the third modification of the piezoelectric actuator.

FIG. 28 is a plan view showing a fourth modification of thepiezoelectric actuator.

FIG. 29 is a diagram showing a manufacturing method of a vibrating plateof the fourth modification.

FIG. 30 is a plan view showing another example of the fourthmodification of the piezoelectric actuator.

FIG. 31 is a plan view showing a fifth modification of the piezoelectricactuator.

FIG. 32 is a plan view showing a sixth modification of the piezoelectricactuator.

FIG. 33 is a diagram for explaining the amplitude of a support member ofthe sixth modification of the piezoelectric actuator.

FIG. 34 is a plan view showing another example of the sixth modificationof the piezoelectric actuator.

FIG. 35 is a plan view showing a seventh modification of thepiezoelectric actuator.

FIG. 36 is a diagram for explaining the position of the center ofrotation of a support member for rotationally supporting a vibratingplate of the seventh modification of the piezoelectric actuator.

FIG. 37 is a diagram for explaining the operation of the vibrating platewhen the rotor is to be rotated in the reverse direction in the seventhmodification.

FIG. 38 is a plan view showing another example of the seventhmodification of the piezoelectric actuator.

FIG. 39 is a plan view showing a further modification of the seventhmodification of the piezoelectric actuator.

FIG. 40 is a diagram showing a conductive construction for supplying adrive voltage to the piezoelectric actuator.

FIG. 41 is a diagram showing a modification of the conductiveconstruction for supplying the drive voltage to the piezoelectricactuator.

FIG. 42 is a side view showing a modification the conductiveconstruction.

FIG. 43 is a diagram showing another modification of the conductiveconstruction for supplying the drive voltage to the piezoelectricactuator.

FIG. 44 is a diagram showing a further modification of the conductiveconstruction for supplying the drive voltage to the piezoelectricactuator.

FIG. 45 is a side view showing a still further modification of theconductive construction.

FIG. 46 is a plan view showing the overall construction of apiezoelectric actuator according to a second embodiment of the presentinvention.

FIG. 47 is a side view showing a vibrating plate that is a component ofthe piezoelectric actuator according to the second embodiment.

FIG. 48 is a plan view showing the vibrating plate of the piezoelectricactuator according to the second embodiment.

FIG. 49 is a diagram showing a construction for supplying electric powerto a piezoelectric element of the vibrating plate of the piezoelectricactuator according to the second embodiment.

FIG. 50 includes a diagram showing a state in which the vibrating plateof the piezoelectric actuator according to the second embodiment causesa longitudinal vibration, and a diagram showing a state in which thevibrating plate causes a bending vibration.

FIG. 51 is a diagram for explaining a driving direction of a rotor whenthe vibrating plate of the piezoelectric actuator according to thesecond embodiment causes a longitudinal vibration.

FIG. 52 is a diagram for explaining a driving direction of the rotorwhen the vibrating plate of the piezoelectric actuator according to thesecond embodiment causes a bending vibration.

FIG. 53 is a plan view showing the overall construction of apiezoelectric actuator according to a third embodiment of the presentinvention.

FIG. 54 is a plan view showing a modification of the piezoelectricactuator according to the third embodiment.

FIG. 55 is a plan view showing the overall construction of apiezoelectric actuator according to a fourth embodiment of the presentinvention.

FIG. 56 is a side view showing the vicinity of a contacting part betweenthe vibrating plate and the rotor of the piezoelectric actuatoraccording to the fourth embodiment.

FIG. 57 is a side view showing the vicinity of the contacting partbetween the vibrating plate and the rotor in a modification of thepiezoelectric actuator according to the fourth embodiment.

FIG. 58 is a diagram for explaining a driving direction of a rotor whena vibrating plate in another modification of the piezoelectric actuatoraccording to the fourth embodiment causes a bending vibration.

FIG. 59 are diagram showing an example of the construction of a drivingcircuit for switching the vibrating plate in the other modification ofthe piezoelectric actuator according to the fourth embodiment between alongitudinal vibration mode and a bending vibration mode.

FIG. 60 is a diagram showing a modification of the piezoelectricactuator according to the first to fourth embodiments.

FIG. 61 is a plan view schematically showing an ultrasonic motor using aconventional piezoelectric actuator.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will now be given of embodiments of the present inventionwith reference to the drawings.

A. First Embodiment

A-1. Overall Construction

FIG. 1 is a plan view showing the principal construction of a calendardisplay mechanism having a piezoelectric actuator incorporated thereinin a wristwatch according to a first embodiment of the presentinvention.

A piezoelectric actuator A1 is generally composed of a vibrating plate10 that extensionally vibrates in an in-plane direction (a directionparallel to the plane of the figure) and a rotor (rotating member) 100.The rotor 100 is rotationally supported on a main plate (support body)103, and is disposed at a position where it abuts against the vibratingplate 10. When its outer peripheral surface is tapped by vibrationsgenerated in the vibrating plate 10, the rotor 100 is rotationallydriven in a direction shown by the arrow in the figure.

Next, a calendar display mechanism is coupled to the piezoelectricactuator A1, and is driven by a driving force thereof. The principalpart of the calendar display mechanism is generally composed of aspeed-reducing wheel train for decelerating the rotation of the rotor100, and a ring-shaped date indicator 50. The deceleration wheel trainincludes an intermediate date wheel 40 and a date indicator drivingwheel 60.

Here, when the vibrating plate 10 vibrates in the in-plane direction asdescribed above, the rotor 100 abutting against the vibrating plate 10is rotated in a clockwise direction. The rotation of the rotor 100 istransmitted to the date indicator driving wheel 60 via the intermediatedate wheel 40, and the date indicator driving wheel 60 rotates the dateindicator 50 in a clockwise direction. In this way, the transmittance ofall forces from the vibrating plate 10 to the rotor 100, from the rotor100 to the speed-reducing wheel train, and from the speed-reducing wheeltrain to the date indicator 50 is effected in the in-plane direction.For this reason, the thickness of the calendar display mechanism can bereduced.

FIG. 2 is a sectional view of a timepiece according to the firstembodiment of the present invention. In the figure, a calendar mechanismincluding the above-described piezoelectric actuator A1 is incorporatedinto the hatched region, and the thickness thereof is considerably thinat about 0.5 mm. A disk-like dial 70 is provided above the calendardisplay mechanism. A window 71 for displaying the date is provided in apart of the outer periphery of the dial 70 so that the date of the dateindicator 50 can be seen through the window 71. In addition, a movement73 for driving hands 72, and a driving circuit (not shown), which willbe described later, are provided below the dial 70.

In the construction as described above, the piezoelectric actuator A1has a construction in which a coil and a rotor are not stacked in thethickness direction as in a conventional stepping motor, but thevibrating plate 10 and the rotor 100 are disposed in the same plane. Forthis reason, it is structurally suited to a reduction in thickness. Forthis reason, the thickness of the calendar display mechanism can bereduced, and the thickness of the entire timepiece can be reduced.Furthermore, the movement 73 can be shared between a timepiece with thecalendar display mechanism and a timepiece without such a displaymechanism, whereby productivity can be improved.

A-2. Construction of Piezoelectric Actuator

Next, a description will be given of the piezoelectric actuator A1according to this embodiment. As shown in FIG. 3, the piezoelectricactuator A1 includes a long plate-like vibrating plate 10 that iselongated in the lateral direction in the figure, and a support member11 for supporting the vibrating plate 10 on the main plate 103 (see FIG.1).

At a longitudinal end 35 of the vibrating plate 10, a projection 36 isprojected toward the rotor 100, and the projection 36 is in contact withthe outer peripheral surface of the rotor 100. With the provision ofsuch a projection 36, an operation such as grinding may be performedonly on the projection 36 in order to maintain the state of the contactsurface between the projection 36 and the rotor 100, so that the contactsurface between the projection 36 and the rotor 100 can be easilycontrolled. In addition, the projection 36 formed of a conductive memberor a non-conductive member may be used. When the projection 36 is formedof a non-conductive member, piezoelectric elements 30 and 31 can beprevented from shorting even if they come into contact with the rotor100 that is generally formed of metal.

As shown in the figure, in this embodiment, the projection 36 is formedin the shape of a curved surface projecting toward the rotor 100 inplane view. By forming the projection 36 abutting against the rotor 100in the shape of a curved surface in this way, even if the positionalrelationship between the rotor 100 and the vibrating plate 10 varies(due to variations in size and the like), the contact state between theouter peripheral surface of the rotor 100 that is a curved surface andthe projection 36 formed in the shape of a curved surface does notchange so much. Therefore, a stable contact state between the rotor 100and the projection 36 can be maintained.

As shown in FIG. 4(a), in this embodiment, the projection 36 is formedin the shape of a curved surface projecting toward the rotor 100 insectional view. On the other hand, a concave surface 100 a in the shapeof a curved surface is formed in the outer peripheral surface of therotor 100 so that the projection 36 and the concave surface 100 a in theshape of a curved surface contact each other. Since the sectionalcontacting structure is such that a curved surface contacts a curvedsurface, a good contact state can be maintained even if the contactangle between the projection 36 and the rotor 100 varies. For example,as shown in FIG. 4(b), if the outer peripheral surfaces of theprojection 36 and the rotor 100 are formed in the shape of straightlines, the contact state is greatly changed by merely a slight variationof the contact angle. Here, although a guide member for guiding theprojection 36 may be provided in order to maintain the contact angleconstant, such a construction causes an increase in the number ofcomponents that increases the cost. Therefore, by forming the projection36 and the concave surface 100 a in the shape of curved surfaces, as inthis embodiment, a good contact state can be maintained without causinga substantial increase in cost. In addition, disengagement of theprojection 36 from the concave surface 100 a can be restrained. Not onlythe concave surface 100 a in the shape of a curved surface but also aV-groove 100 b may be formed in the outer peripheral surface of therotor 100, as shown in FIG. 5. In this case, variations of the contactangle between the projection 36 and the rotor 100, and the disengagementof 36 from the V-groove 100 b can also be reduced.

Returning to FIG. 3, one end portion (mounting portion) 37 of thesupport member 11 is mounted on the vibrating plate 10 at a portionslightly toward the rotor 100 from the longitudinal center thereof. Theother end (fixed portion) 38 of the support member 11 is supported onthe main plate 103 (see FIG. 1) by a screw 39. In such a construction,the support member 11 supports the vibrating plate 10 in a state ofurging, by its elastic force, toward the rotor 100, whereby theprojection 36 of the vibrating plate 10 is brought into abutment withthe side surface of the rotor 100.

As shown in FIG. 6, the vibrating plate 10 has a stacked structure inwhich a reinforcing plate 32, such as stainless steel, havingsubstantially the same shape as the piezoelectric elements 30 and 31,and having a thickness smaller than that of the piezoelectric elements30 and 31, is arranged between the two rectangular piezoelectricelements 30 and 31. By arranging the reinforcing plate 32 between thepiezoelectric elements 30 and 31 in this way, damage of the vibratingplate 10 due to the excessive vibration of the vibrating plate 10 or anexternal force can be reduced. In addition, the reinforcing plate 32having a thickness smaller than that of the piezoelectric elements 30and 31 is used so as to allow as much vibration as possible of thepiezoelectric elements 30 and 31.

Electrodes 33 are disposed on the surfaces of the piezoelectric elements30 and 31 that are disposed at the upper and lower side surfaces. Avoltage is supplied from a conductive construction, which will bedescribed later, to the piezoelectric elements 30 and 31 via theelectrodes 33. Here, as the piezoelectric elements 30 and 31, varioustypes of substances can be used, such as lead zirconate titanate(PZT(trademark), quartz, lithium niobate, barium titanate, leadtitanate, lead metaniobate, polyvinylidene fluoride, zinc lead niobate((Pb(Zn1/3-Nb2/3)O3 1-x-Pb Ti O3 x), wherein x varies with thecomposition, and x is about 0.09), and scandium lead niovate((Pb((Sc1/2Nb1/2)1-x Tix))O3), wherein x varies with the composition,and x is about 0.09).

In addition, in this embodiment, each of the electrodes 33 is formedwith a thickness of 0.5 μm or more. Electrodes each having a thicknessof about 0.1 to 0.3 μm are usually formed on such a piezoelectricelement. In the piezoelectric actuator A1, however, electrodes thickerthan common electrodes are formed, whereby the electrodes 33 serve thefunction of a reinforcing material against bending in addition to thefunction of the electrode so as to improve the strength of the vibratingplate 10. Here, although the strength is improved when the thickness ofeach of the electrodes 33 is increased, an excessive increase in thethickness will prevent the vibration of the vibrating plate 10.Therefore, when the improvement of the strength and the influence on thevibration are considered, the thickness of each of the electrodes 33 maypreferably be 0.5 μm or more, and the sum of the thicknesses of theelectrodes 33 formed on the upper and lower surfaces may preferably bethe thickness of the reinforcing plate 32 or less. In the case of thepiezoelectric actuator A1 to be incorporated into the calendar displaymechanism of the wristwatch as in this embodiment, when the reduction inthickness, the influence on the vibration, and the strength and the likeare considered, the thickness of the reinforcing plate 32 may be about0.1 mm. Therefore, in this case, the sum of the thicknesses of theelectrodes 33 may be 0.1 mm or less.

When an alternating voltage is applied from a driving circuit, whichwill be described later, to the piezoelectric elements 30 and 31 via theelectrodes 33, the thus-constructed vibrating plate 10 vibrates as thepiezoelectric elements 30 and 31 expand and contract. In this case, thevibrating plate 10 causes a longitudinal vibration such that it expandsand contracts in the longitudinal direction, as shown in FIG. 7, wherebythe vibrating plate 10 vibrates in the direction shown by abi-directional arrow in FIG. 3 (an unloaded state, that is, a state inwhich the projection 36 is not in contact with the rotor 100). Inaddition, as shown in FIG. 8, the vibrating plate 10 has a structure inwhich the long plate-like piezoelectric elements 30 and 31 are stacked,and the piezoelectric elements 30 and 31 are driven while beingconnected in parallel so that they are polarized in opposite directions(shown by the arrow in the figure), whereby the amplitude of vibrationcaused by the vibrating plate 10 can be amplified, and a greaterdisplacement can be obtained. On the other hand, if the piezoelectricelements 30 and 31 are driven while being connected in series so thatthey are polarized in the same direction, as shown in FIG. 9, thevibrating plate 10 can be vibrated with a low current. Therefore, theconnecting structure of the piezoelectric elements 30 and 31 may bedetermined in accordance with the conditions of using the piezoelectricactuator A1 (when an increase in displacement is regarded as important,or when a reduction in power consumption is regarded as important).

A-3. Operation of Piezoelectric Actuator

Next, a description will be given of the operation of the piezoelectricactuator constructed as described above. Firstly, when a voltage isapplied to the vibrating plate 10 from a driving circuit (not shown),the vibrating plate 10 causes a flexural vibration as the piezoelectricelements 30 and 31 expand and contract, and vibrates in the direction ofthe arrow with the projection 36 abutting against the rotor 100, asshown in FIG. 3. The rotor 100 is rotated in the direction of the arrowin accordance with the displacement of the projection 36 caused by thevibration. The rotor 100 is rotated in this way, whereby the dateindicator 50 is rotated via the intermediate date wheel 40 (see FIG. 1),and the date and the day to be displayed are changed.

Here, in the piezoelectric actuator A1, the projection 36 abuttedagainst the rotor 100 is provided at a position shifted from the centerline shown by a one-dot chain line in FIG. 3 in the widthwise direction(vertical direction in FIG. 3) of the vibrating plate 10. Therefore, abending vibration shown in FIG. 10 is generated in the vibrating plate10 by a reaction force from the side surface of the rotor 100. If theabove-described bending vibration is induced in addition to thelongitudinal vibrations of the piezoelectric elements 30 and 31 causedby the application of a voltage, the projection 36 moves along anelliptical orbit, as shown in FIG. 11. That is, if the bending vibrationis excited in addition to the longitudinal vibration, a greaterdisplacement can be obtained. If the displacement of the projection 36can be amplified in this way, driving efficiency of the rotor 100 thatis driven in accordance with the displacement can be improved. Theposition where the projection 36 is provided is not limited to theposition shown in the figure, and the projection 36 may be provided at aposition where a bending vibration can be induced in the substantiallyrectangular vibrating plate 10 by the reaction force of theabove-described rotor 100.

Furthermore, if the vibrating plate 10 is used which has a shape suchthat the resonance frequency of the longitudinal vibration substantiallycoincides with the resonance frequency of the bending vibration, theprojection 36 can be moved along a larger elliptical orbit. If theprojection 36 is moved along the large elliptical orbit in this way, thetime the projection 36 comes into contact with the rotor 100 iselongated, whereby the displacement of the projection 36 during contactis amplified. Therefore, if a bending vibration that resonates with thelongitudinal vibration due to the expansion and contract of thepiezoelectric elements 30 and 31 is induced, the driving force can betransmitted with higher efficiency.

As described above, while the vibrating plate that has a shape such thatthe longitudinal vibration and the bending vibration generated in thevibrating plate 10 resonate may be used, a vibrating plate that has ashape such that the resonance frequency of the bending vibration of thevibrating plate 10 is increased to be slightly higher than the resonancefrequency of the longitudinal vibration may be used. If the resonancefrequency of the bending vibration is increased to be slightly higherthan the resonance frequency of the longitudinal vibration in this way,a bending vibration is generated in the vibrating plate 10, as shown inFIG. 10, whereby the projection 36 can be greatly displaced, and thevibration generated in the vibrating plate 10 can be stabilized. This isbecause the bending vibration cannot follow the longitudinal vibrationwhen the resonance frequency of the bending vibration generated inaccordance with the longitudinal vibration is lower than the resonancefrequency of the longitudinal vibration generated by the voltage appliedto the piezoelectric elements 30 and 31, and all vibrations generated inthe vibrating plate 10 become unstable. In addition, in a vibratingplate in which the resonance frequency of the bending vibration greatlydiffers from the resonance frequency of the longitudinal vibration,amplitudes of the longitudinal vibration and bending vibration generatedin the vibrating plate decrease, whereby driving efficiency is lowered.Therefore, if the resonance frequency of the bending vibration of thevibrating plate is slightly higher than the resonance frequency of thelongitudinal vibration, a decrease in the amplitude of the vibrationgenerated in the vibrating plate 10, that is, the displacement of theprojection 36, can be restricted, and a stable vibration can begenerated. For example, when a vibrating plate having the varyingimpedance characteristics shown in FIG. 12 was used, it wasexperimentally recognized that the projection 36 greatly displaced alongthe above-described elliptical orbit, and a stable vibration wasgenerated in the vibrating plate. In the vibrating plate having thecharacteristics shown in FIG. 12, the resonance frequency at the minimumvalue of the impedance of the longitudinal vibration is 284.3 kHz, andthe resonance frequency at the minimum value of the impedance of thebending vibration is 288.6 kHz. Therefore, if the vibrating plate 10 inwhich the resonance frequency of the bending vibration of the vibratingplate 10 is increased to be higher than the resonance frequency of thelongitudinal frequency by about 2% is used, the above-describedadvantages can be obtained. In a case where the resonance frequency ofthe bending vibration is slightly increased in this way, if thevibrating plate 10 is excited with a frequency between the resonancefrequency of the longitudinal vibration and the resonance frequency ofthe bending vibration, that is, if the piezoelectric elements 30 and 31are driven with an exciting frequency within such a range, both thelongitudinal vibration and the bending vibration can be easily induced,and a vibration such that the elliptical orbit shown in FIG. 11 becomeslarge can be generated in the vibrating plate 10, whereby the rotor 100can be rotationally driven with higher efficiency.

While the bending vibration may be induced in the vibrating plate 10 bya reaction force from the rotor 100, as described above, the projection36 that is an abutment portion of the rotor 100 and the vibrating plate10 may be elastically deformed in the widthwise direction by a reactionforce from the rotor 100 generated by the longitudinal vibration of thevibrating plate 10 so that the projection 36 is moved along theabove-described elliptical orbit.

Since the projection 36 is urged toward the rotor 100 by the elasticforce of the support member 11 in the piezoelectric actuator A1,sufficient friction can be obtained between the rotor 100 and theprojection 36. This reduces slippage of the projection 36 and the rotor100, whereby a large driving force can be stably transmitted from theprojection 36 to the rotor 100.

Since the rotor 100 and the vibrating plate 10 are supported on the mainplate 103, which is a single member, the spacing arrangement betweenthem is maintained constant. Therefore, the contact state between theprojection 36 and the rotor 100 can be stably maintained, whereby thedriving force can be stably transmitted.

In the piezoelectric actuator A1 according to this embodiment, the end37 of the support member 11 is attached to the vibrating plate 10 at aposition of a node of amplitude of the center lines of vibrating plate10 shown by broken lines in FIG. 13, that is, at a position of minimumamplitude. More specifically, the end 37 is attached to the vibratingplate 10 slightly toward the rotor 100 from the longitudinal centralpart. This is because while the position of the center of gravity of thevibrating plate 10, i.e., the longitudinal central position of therectangular vibrating plate 10 is a node of vibration during theunloaded state, the node of vibration of the vibrating plate 10 isactually located toward the rotor 100 from the central part, as shown inFIG. 13 due to the influence of the reaction force and the like from therotor 100 as described above. The vibrating plate 10 is supported at theposition of the node of vibration in this way, whereby loss of vibrationenergy is decreased and the driving force can be transmitted with higherefficiency. In addition, if the position of a node of vibration of thesupport member 11 in accordance with the vibration of the vibratingplate 10 is allowed to substantially coincide with the end 37 of thesupport member 11, the loss of the vibration energy can be furtherdecreased. When the vibrating plate 10 does not have a rectangular shapeshown in FIG. 10, the vibrating plate 10 may be supported at a portiontoward the rotor 100 from the center of gravity of the vibrating plate10. This is because the node of the vibration of the vibrating plate 10is moved toward the rotor 100 from the center of gravity of thevibrating plate 10 by the influence of the reaction force and the likefrom the rotor 100. The support member 11 may support the vibratingplate 10 at the position of the node.

Furthermore, in the piezoelectric actuator A1 according to thisembodiment, the vibrating plate 10 having a structure in which thepiezoelectric elements 30 and 31 and the reinforcing plate 32 arestacked can rotationally drive the rotor 100 without using theamplifying member.

Therefore, the construction is simplified, and the size of the devicecan be easily reduced. In addition, mechanical components of thepiezoelectric actuator A1 are the vibrating plate 10, the support member11, and the like, and components are not stacked in the thicknessdirection (direction perpendicular to the plane of FIG. 1). Therefore,the thickness of the device can be easily reduced.

In addition, in the piezoelectric actuator A1, the rotor 100 is drivenonly in one direction shown by the arrow in the figure, and anothervibrating plate for driving the rotor 100 in the opposite direction, anda mechanism for changing the direction of abutment of the vibratingplate against the rotor 100 are not provided, that is, there are fewfactors for preventing the vibration of the vibrating plate 10.Therefore, the driving force can be transmitted more efficiently.

In the piezoelectric actuator A1 according to this embodiment, since therotor 100 is driven only in one direction, it is necessary to restrictthe rotation of the rotor 100 in the opposite direction. However, when alarge external force is applied or a load is increased, the rotor 100sometimes tends to rotate in the opposite direction against the drivingforce generated by the vibrating plate 10. For example, when an oppositetorque exceeding the frictional force between the projection 36 and therotor 100 is generated, both of the projection 36 and the rotor 100 slipagainst each other to allow the rotor 100 to be rotated in the oppositedirection. In the piezoelectric actuator A1 according to thisembodiment, however, since the support member 11 is not a rigid body butis elastic, as shown in FIG. 14, when a force which tends to rotate therotor 100 in the opposite direction increases and the rotor 100 ispushed back in the opposite direction, the rotation of the rotor 100 inthe opposite direction and the rotation of the vibrating plate 10 withthe projection 36 contacting the rotor 100 are allowed. As shown in FIG.15, in this embodiment, the center of rotation allowed for the vibratingplate 10 is set to be located within a quadrant formed by the line Bextending from the contact point A of the rotor 100 and the projection36 in a direction opposite to the driving direction of the rotor 100 atthe point A and the line C intersecting the line B at right angles onthe point A. That is, the rotation of the vibrating plate 10 around theend 38 of the support member 11 located within the above-describedquadrant is allowed. By providing the center of rotation at such aposition, when the vibrating plate 10 is rotated clockwise in the figurein accordance with the opposite rotation of the rotor 100, theprojection 36 is displaced toward the rotor 100 as if to cut into therotor 100. Therefore, the force of the projection 36 pressing againstthe rotor 100 is increased, whereby the friction between the projection36 and the rotor 100 is increased. This makes it possible to transmit alarge torque (for the normal rotation) from the vibrating plate 10,whereby the rotation of the rotor 100 in the opposite direction due toan increase in load and the external force can be inhibited. That is,when the load is increased, the driving torque can be increasedcorresponding to the increase in the load. When the force in theopposite direction is eliminated or decreased, the vibrating plate 10 isreturned to the lower position shown by the one-dot chain line in FIG.14 by the elastic force of the support member 11.

In addition to the increase in friction between the projection 36 andthe rotor 100, when the rotor 100 tends to rotate in the oppositedirection, the vibrating plate 10 may be rotated so that the projection36 moves away in a direction opposite to the driving direction shown bythe arrow in accordance with the movement of the rotor 100, as shown inFIG. 16. In order to rotate the vibrating plate 10 in this way, thecenter of rotation of the vibrating plate 10 may be set to be locatedwithin a quadrant formed by the line D extending from the contact pointA of the rotor 100 and the projection 36 in the driving direction of therotor 100 at the point A and the line C intersecting the line D at rightangles on the point A. This makes it possible to rotate the vibratingplate 10 so that the projection 36 moves away as described above,whereby damage of the rotor 100 and the projection 36 due to theexternal force and the like can be reduced.

A-4. Construction of Calendar Display Mechanism

Next, a description will be given of the construction of the calendardisplay mechanism with reference to FIG. 1 and FIG. 17, which is asectional view of FIG. 1. In the figures, the main plate 103 is a firstbottom plate for arranging parts thereon, and a main plate 103′ is asecond bottom plate partially having a stepped portion with respect tothe main plate 103. A gear 100 c that is coaxial with the rotor 100 andis rotated with the rotor 100 is provided above the rotor 100. Theintermediate date wheel 40 is composed of a large diameter section 4 band a small diameter section 4 a that is fixed so as to be concentricwith the large diameter section 4 b and is formed slightly smaller thanthe large diameter section 4 b. In accordance with the rotation of thegear 100 c with the rotor 100, the large diameter section 4 b thatmeshes with the gear 100 c is rotated, whereby the intermediate wheel 40is rotated. A peripheral surface of the small diameter section 4 a iscut out in substantially a square shape to form a cutout 4 c. A shaft 41of the intermediate date wheel 40 is formed on the main plate 103′, anda bearing (not shown) coupled to the shaft 41 is formed inside theintermediate date wheel 40. Therefore, the intermediate date wheel 40rotationally provided on the main plate 103′. The rotor 100 also has abearing (not shown) formed inside thereof, and is rotationally supportedon the main plate 103.

Next, the date indicator 50 is formed in the shape of a ring, and aninternal gear 5 a is formed on the inner peripheral surface thereof. Thedate indicator driving wheel 60 has a gear of five teeth, and mesheswith the internal gear 5 a. A shaft 61 is provided in the center of thedate indicator driving wheel 60 to rotationally support the dateindicator driving wheel 60. The shaft 61 is loosely inserted into athrough hole 62 formed in the main plate 103′. The through whole 62 iselongated along the circumferential direction of the date indicator 50.

One end of a plate spring 63 is fixed to the main plate 103′, and theother end is fixed to the shaft 61. This allows the plate spring 63 tourge the shaft 61 and the date indicator driving wheel 60. Swinging ofthe date indicator 50 is prevented by the urging action of the platespring 63.

One end of a plate spring 64 is secured to the main plate 103′ by ascrew, and the other end is bent in substantially a V shape to form anend part 64 a. A contact 65 is arranged so as to come into contact withthe plate spring 64 when the intermediate date wheel 40 is rotated andthe end part 64 a enters into the cutout 4 c. A predetermined voltage isapplied to the plate spring 64, and the voltage is also applied to thecontact 65 upon contacting the contact 65. Therefore, by detecting thevoltage of the contact 65, a date feed state can be detected. A manualdriving wheel meshing with the internal gear 5 a may be provided so thatthe date indicator 50 is driven when a user performs a predeterminedoperation on a crown (not shown).

A-5. Operation of Calendar Display Mechanism

A description will be given of an automatic calendar-updating operationwith reference to FIG. 1. When it is twelve o'clock midnight each day,this is detected, and a driving signal V is supplied to thepiezoelectric elements 30 and 31 from a driving circuit 500, which willbe described later. Then, the vibrating plate 10 vibrates as describedabove. This makes the rotor 100 rotate in a clockwise direction, and,following this, the intermediate date wheel 40 starts rotation in acounterclockwise direction.

Here, the driving circuit 500 is constructed so as to stop the supply ofthe driving signal V when the plate spring 64 comes into contact withthe contact 65. In a state where the plate spring 64 is in contact withthe contact 65, the end portion 64 a enters into the cutout 4 c.Therefore, the intermediate date wheel 40 starts to rotate.

Since the date indicator driving wheel 60 is urged in a clockwisedirection by the plate spring 63, the small diameter section 4 a isrotated while sliding on teeth 6 a and 6 b of the date indicator drivingwheel 60. When the cutout 4 c reaches the position of the tooth 6 a ofthe date indicator driving wheel 60 during the rotation, the tooth 6 ameshes with the cutout 4 c. In this case, the circumscribed circle ofthe date indicator driving wheel 60 has moved to the position shown byC1.

When the intermediate date wheel 40 is continuously rotated in acounterclockwise direction, the date indicator driving wheel 60 isrotated in a clockwise direction by one tooth, that is, by “⅕” of arevolution operatively associated with the intermediate date wheel 40.Furthermore, the date indicator 50 is rotated in a clockwise directionby one tooth (equivalent to the date range for one day) operativelyassociated with the rotation of the date indicator driving wheel 60. Inthe final day of a month having a number of days less than “31”, theabove operation is repeated a plurality of times, and the correct datebased on a calendar is displayed by the date indicator 50.

When the intermediate date wheel 40 is continuously rotated in acounterclockwise direction, and the cutout 4 c reaches the end part 64 aof the plate spring 64, the end 64 a enters into the cutout 4 c. Then,the plate spring 64 comes into contact with the contact 65, the supplyof the driving signal V is stopped, and the rotation of the intermediatedate wheel 40 is stopped. Therefore, the intermediate date wheel 40 isrotated once a day.

Incidentally, the load of the piezoelectric actuator A1 increases during1) a first period (start of rotation) until the end 64 a of the platespring 64 gets out of the state where it is in the cutout 4 c, and 2) asecond period in which the cutout 4 c meshes with the date indicatordriving wheel 60 to rotate the date indicator 50. When the load of thepiezoelectric actuator A1 increases, slippage between the rotor 100 andthe projection 36 is increased, and in the worst case, it becomesimpossible to drive the rotor. In the mechanism of this embodiment,however, the first period and the second period do not overlap eachother. That is, the maximum torque time required for detecting the datefeed state and the maximum torque time required for driving the dateindicator 50 are staggered. Therefore, the peak current of thepiezoelectric actuator A1 can be suppressed, and consequently, thetimepiece can be positively operated by maintaining the power sourcevoltage above a certain voltage value.

A-6. Driving Circuit

FIG. 18 is a block diagram of the driving circuit 500 for applying avoltage to the piezoelectric elements 30 and 31, and FIG. 19 is a timingchart of the driving circuit 500. A twelve o'clock midnight detectionunit 501 is a mechanical switch incorporated in the movement 73 (seeFIG. 2), and outputs a first control pulse CTLa shown in FIG. 19(a) whenit is twelve o'clock midnight. A date feed detection unit 52 has theabove-described plate spring 64 and the contact 65 as principalsections, and outputs a second control pulse CTLb shown in FIG. 19(b)when the plate spring 64 comes into contact with the contact 65.

A control circuit 503 generates an oscillation control signal CTLc (seeFIG. 19(c)) based on the first control pulse CTLa and the second controlpulse CTLb. The control circuit 503 may be composed of, for example, anSR flip flop so that the first control pulse CTLa is supplied to setterminals, and the second control pulse CTLb is supplied to resetterminals. In this case, as shown in FIG. 19(c), when the first controlpulse CTLa rises from a low level to a high level, the oscillationcontrol signal CTLc changes from a low level to a high level, and thisstate is maintained until the second control pulse CTLb rises, when itchanges from the high level to the low level.

The oscillation circuit 504 is constructed so that an oscillationfrequency is substantially equal to fs(n) wherein n represents the orderof the vibration mode of the vibrating plate 10. The oscillation circuit504 may be formed by, for example, a Colpitts oscillation circuit.

Power supplied to the oscillation circuit 504 is controlled by theoscillation control signal CTLc. The power supply is effected when theoscillation control signal CTLc is at the higher level, and is stoppedwhen the oscillation control signal CTLc is at the lower level.Therefore, a waveform of the driving signal V, which is an output of theoscillation circuit 504, oscillates when the oscillation control signalCTLc is at a higher level, as shown in FIG. 19(d).

While the intermediate date wheel 40 is rotated once a day as describedabove, the period thereof is limited, starting from twelve o'clockmidnight. Therefore, the oscillation circuit 504 may sufficientlyoscillate only during the period. In the driving circuit 50 of thisembodiment, the power supply to the oscillation circuit 504 iscontrolled by the oscillation control signal CTLc to thereby completelystop the operation of the oscillation circuit 504 during a period inwhich there is no need for rotating the intermediate date wheel 40.Therefore, power consumption of the oscillation circuit 504 can bereduced.

A-7. Modifications of Piezoelectric Actuator

In place of the piezoelectric actuator A1 having the construction asdescribed above, it is possible to use the following variously modifiedpiezoelectric actuators, and it is also possible to use a piezoelectricactuator formed as a combination of the modifications.

A-7-1. First Modification

While the projection 36 is provided on the vibrating plate 10 at acontacting part between the projection 36 and the rotor 100 in thepiezoelectric actuator A1 shown in the above-described embodiment, acutout 90 may be formed by cutting out a peak of a rectangular vibratingplate 10 on the side of the rotor 100 so that the cutout 90 is broughtinto abutment with the side surface of the rotor 100, as shown in FIG.20. In this case, a surface state of the cutout 90 can be easilycontrolled in a manner similar to the above-described projection 36. Byforming the cutout 90 in the shape of a curved surface, a good contactstate can be maintained in a manner similar to the above-describedpiezoelectric actuator A1.

A-7-2. Second Modification

While the electrodes 33 are provided on the entire surfaces of thepiezoelectric elements 30 and 31 in the above-described embodiment,electrodes 33 may be disposed only near the longitudinal central partsof the piezoelectric elements 30 and 31 and may not be disposed on bothends, as shown in FIG. 21. That is, the piezoelectric elements 30 and 31may be constructed so as to have electrode sections having electrodes onthe surfaces thereof, and non-electrode sections located on both ends ofthe electrode sections. This construction makes it possible to reducethe drive voltage while maintaining the driving force to the rotor 100.This is because, when the vibrating plate 10 is vibrated with itsnatural vibration frequency, the both ends of the vibrating plate 10 aresufficiently greatly displaced by the vibration, and the displacement isnot amplified even if a voltage is applied to the displaced portions soas to expand and contract the piezoelectric elements 30 and 31 providedon the both ends.

As shown in FIG. 22, the electrodes 33 may be disposed only on thewidthwise (vertical direction in the figure) central part of thepiezoelectric elements 30 and 31, and may not be disposed on thewidthwise both ends (upper and lower sides in the figure).

A-7-3. Third Modification

While the rectangular vibrating plate 10 is used in the above-describedembodiment, a tapered vibrating plate 95 having a small thickness on theside of the rotor 100 may be used. When preparing the vibrating plate 95having such a shape, tapered piezoelectric elements and reinforcingplate may be stacked in a manner similar to the above-describedvibrating plate 10. The use of such a vibrating plate 95 amplifies thedisplacement of an end 96 of the vibrating plate 95 on the side of therotor 100, whereby the rotor 100 can be driven at high speed. Inaddition, since the lengths in the widthwise direction that is thevertical direction of the figure are not uniform, the widthwiseresonance of the vibrating plate 95 can be restricted, that is, thevibration in the widthwise direction, can be reduced.

In addition, a vibrating plate 97 having a shape shown in FIG. 24 may beused. As shown in the figure, the vibrating plate 97 is, unlike thetotally tapered vibrating plate 95, partially (in the figure, the sideof the rotor 100) tapered. The use of the vibrating plate having such ashape makes it possible to drive the rotor 100 at high speed in a mannersimilar to the vibrating plate 95 shown in FIG. 23, compared with therectangular vibrating plate 10.

In addition, when a vibrating plate having a shape such that thethickness decreases toward the rotor 100 is used, the rotor 100 can bedriven at high speed. For example, a vibrating plate 98 having a shapeshown in FIG. 25 may be used.

While the vibrating plates shown in FIGS. 23 to 25 are suitable fordriving the rotor 100 at high speed, a vibrating plate 99 having theshape shown in FIG. 26 may be used when the rotor is driven at low speedand high torque. As shown in the figure, the vibrating plate 99 has ashape such that the width increases toward the rotor 100. In thevibrating plate 99, while displacement of an end 96 that is a contactingpart between the end 96 and the rotor 100 is reduced, compared with therectangular vibrating plate 10, torque which tends to rotate the rotor100 is increased, whereby a low-speed drive with high torque can beeffected.

When a vibrating plate having a shape other than the rectangular shapeshown in FIGS. 23 to 26 is used, the electrodes provided on the upperand lower surfaces thereof may have a rectangular shape. For example, asshown in FIG. 27, when a rectangular electrode is formed on thevibrating plate 95, a high-speed drive with low drive voltage can beeffected.

A-7-4. Fourth Modification

As shown in FIG. 28, a horn part (extended part) 110 extending towardthe rotor 100 from the vibrating plate 10 may be provided. Whenproviding such a horn part 110, the reinforcing plate 32 may be preparedin the shape including the horn section 110, as shown in the figure, andthe piezoelectric elements 30 and 31 may be stacked on the upper andlower sides of the reinforcing plate 32, respectively. When thevibrating plate 10 is vibrated in this construction, the vibrating plate10 and the horn part 110 vibrate with amplitude shown by broken lines inFIG. 28. Therefore, the displacement of the tip of the horn part 110abutting against the rotor 100 is amplified, whereby the driving forcecan be efficiently provided. The horn part 110 may have a shape shown inFIG. 30.

A-7-5. Fifth Modification

As shown in FIG. 31, the vibrating plate 10, the support member 11 andthe rotor 100 may be disposed so that the end 38 of the support member11 is located on a tangent to the projection 36 of the vibrating plate10 and the rotor 100, i.e., on the line S perpendicular to the directionof a pressing force F from the projection 36 to the rotor 100 in theinitial vibration state. When the vibrating plate 10, the support plate11, and the rotor 100 are disposed so as to achieve such a positionalrelationship, the contact position and the angle between the rotor 100and the projection 36 are not changed even if fine adjustment of thepositions of the support member 11 and the vibrating plate 10 iseffected around the end 38 secured by the screw 39 in order to adjustthe pressing force and the like of the projection 36 to the rotor 100,whereby the driving force can always be stably provided. In addition,variations in the contact angle between the vibrating plate and therotor due to the shape, the position, the change with the passage oftime, and the like can be prevented.

A-7-6. Sixth Modification

As shown in FIG. 32, the longitudinal both ends of the vibrating plate10 may be supported by two support members 11. This can restrict thevibration of the vibrating plate 10 in the widthwise direction (verticaldirection in the figure), that is, the vibration that prevents thevibration in the horizontal direction in the figure required for drivingthe rotor 100 can be restricted. In this case, if the end 37 of thesupport member 11 substantially coincides with the position of anantinode of vibration of the support member 11 in accordance with thevibration of the vibrating plate 10, as shown in FIG. 33, for example,if the length of the support member 11 is set to be a quarter of thevibration wavelength of the support member 11, the prevention of thevibration in the horizontal direction in the figure that is alongitudinal direction of the vibration plate 10 is reduced, wherebyefficiency is further improved.

In addition, when supporting the vibrating plate 10 by the two supportmembers 11 as shown in FIG. 34, the position of the node of thevibration of the vibrating plate 10 may be supported by one (the rightside in the figure) of the two support members 11, and an end of thevibrating plate 10 on the side of the rotor 100 may be supported by theother one (the left side in the figure) of the support members 11. Sinceone of the support members 11 supports the node of the vibration, thiscan reduce the loss of vibration energy, and the other one of thesupport members 11 can restrict the vibration in the widthwise directionnear the contacting part between the support member 11 and the rotor100.

A-7-7. Seventh Modification

While the support member 11 urges the vibration plate 10 toward therotor 100 in the above-described embodiment, the vibrating plate 10 maybe urged toward the rotor 100 by providing a spring member (elasticmember) 180, as shown in FIG. 35. As shown in the figure, the supportmember 11 is mounted on the upper side of the vibrating plate 10, andone end of the spring member 180 is mounted on the lower side of thevibrating plate 10. The other end of the spring member 180 is supportedby a pin 181 provided on the main plate 103 (see FIG. 1). This allowsthe vibrating plate 10 to be urged toward the rotor 100, upper side inthe figure, whereby the projection 36 is brought into abutment with theside surface of the rotor 100. The spring member 180 is provided so asto urge the vibrating plate 10 toward the rotor 100 in this way, thedriving force can be stably transmitted in a manner similar to thepiezoelectric actuator A1 in the above-described embodiment.

When the support member 11 for supporting the vibrating plate 10 and thespring member 180 for urging the vibrating plate 10 toward the rotor 100are provided in this way, the vibrating plate 10 may also be provided soas to be rotated around the position (for example, the position of theend 38 as shown in the figure) within a quadrant formed by the line Band the line C, as shown in FIG. 36, in a manner similar to theabove-described embodiment. Even if the rotor 100 tends to be rotated inthe opposite direction due to the external force, this constructionallows the vibrating plate 10 to return to the former position after itis rotated in accordance with the rotation of the rotor 100 in theopposite direction, and the rotor 100 returns to a normal direction inaccordance with the return of the vibrating plate 10, as shown in FIG.37, whereby the rotation of the rotor 100 in the opposite direction canbe restricted.

Incidentally, when the support member 11 and the spring member 180 areprovided in this way, the vibrating plate 10 may also be formed in atapered shape, as shown in FIG. 38, and the horn part (see FIG. 28) maybe provided.

As shown in FIG. 39, an elastic support member 600 that is a combinationof a support member for supporting the vibrating plate 10 and a springmember for urging the vibrating plate 10 toward the rotor 100 may beprovided. As shown in the figure, the elastic support member 600 is anL-shaped member, and has a support portion 600 a for supporting thevibrating plate 10 and a spring portion 600 b extending from the supportportion 600 a while being bent thereat. The elastic support member 600is supported by a screw 39 at a portion that is an intermediate partbetween the support portion 600 a and the spring portion 600 b, and anend of the spring portion 600 b is supported by the pin 181, whereby thevibrating plate 10 is urged toward the rotor 100. This brings theprojection 36 into abutment with the outer peripheral surface of therotor 100. In addition, slight rotation of the elastic support member600 around the screw 39 is allowed, whereby the rotation of the rotor100 in the opposite direction can be restricted in a manner similar tothe piezoelectric actuator A1.

A-7-8. Eighth Modification

While the vibrating plate has a structure in which the piezoelectricelements 30 and 31 are stacked on the upper and lower sides of thereinforcing plate 32 in the above-described embodiment, the vibratingplate may have a simple structure in which one piezoelectric element isstacked on a reinforcing plate. In addition, three or more piezoelectricelements may be stacked.

A-8. Conductive Construction to Piezoelectric Actuator

Next, a description will be given of a conductive construction forsupplying a drive voltage from the driving circuit 500 to thepiezoelectric elements in the piezoelectric actuators of theabove-described various modifications. Power can be usually supplied tothe piezoelectric elements by wiring the electrodes 33 provided on thevibrating plate 10 from the driving circuit 500. For the purpose ofsimplifying the conductive construction, however, power may be suppliedto the piezoelectric elements by various conductive constructions, asshown in FIGS. 40 to 45.

While the vibrating plate 10 has a structure in which the piezoelectricelements 30 and 31 are stacked on the upper and lower sides of thereinforcing plate 32 in the above-described piezoelectric actuator A1, apiezoelectric actuator shown in FIG. 40 has a structure in whichreinforcing plates 32 are stacked on the upper and lower sides of onepiezoelectric element 251. The reinforcing plate 32 of the upper layeris supported by a support member 11 a, the reinforcing plate 32 of thelower layer is supported by a support member 11 b, and the reinforcingplates 32, the support members 11 a and 11 b are formed of conductivematerials. In this construction, the drive voltage from the drivingcircuit 500 is supplied to the piezoelectric element 251 via the supportmembers 11 a and 11 b and the reinforcing plates 32. This allows thesupport members 11 a and 11 b to serve the conducting function ofsupplying the drive voltage to the piezoelectric element 251, inaddition to the function of supporting the vibrating plate 10 whileurging toward the rotor 100. Therefore, the need to separately provide aconductive construction, such as wiring, for supplying the drive voltageto the piezoelectric element 251 is eliminated, whereby the constructionis simplified. In addition, when another conductive component isprovided, the conductive component may prevent the vibration of thevibrating plate 10. This conductive construction, however, does notencounter such a problem, and the driving force can be efficientlytransmitted.

In addition, as shown in FIGS. 41 and 42, when a vibrating plate 10 inwhich piezoelectric elements 30 and 31 are stacked on the upper andlower sides of a reinforcing plate 32 is used, the drive voltage may besupplied from the driving circuit 500 to the piezoelectric elements 30and 31 via support members 11 c and 11 d formed of a conductivematerial.

As shown in FIGS. 41 and 42, the support member 11 c is formed in theshape to branch into two on the side of the vibrating plate 10, and hasan upper end 260 branched to the upper side (near side of the plane ofFIG. 41) and a lower end 261 branched to the lower side (far side of theplane of the figure). The upper end 260 is attached by solder or aconductive bonding agent to an electrode 33 formed on the surface of thepiezoelectric element 30, and the lower end 261 is attached by solder ora conductive to an electrode 33 formed on the surface of thepiezoelectric element 31. On the other hand, the support member 11 d isattached to the reinforcing plate 32, whereby the drive voltage issupplied from the driving circuit 500 to the piezoelectric elements 30and 31. In this case, the support members 11 c and 11 d also serve thefunction of supporting the vibrating plate 10 and serve the conductingfunction to the piezoelectric elements 30 and 31, as described above,whereby the construction is simplified, and the driving force can beefficiently transmitted.

While the drive voltage may be supplied from the driving circuit to thepiezoelectric elements via the support members formed of the conductivematerial as described above, the drive voltage may be supplied to thepiezoelectric elements by a conductive construction shown in FIG. 43. Asshown in the figure, in the conductive construction, the upper and lowersurfaces (electrodes 33) of the vibrating plate 10 are clamped by aC-shaped elastic conductive member 280, and wiring is connected from thereinforcing plate 32 to the driving circuit 500. If such an elasticconductive member 280 is used, the drive voltage can be supplied fromthe driving circuit 500 to the piezoelectric elements 30 and 31 that arestacked on the upper and lower sides even with a simple construction.

As shown in FIGS. 44 and 45, a wire 290 may be wound around thevibrating plate 10 so that the drive voltage is supplied to thepiezoelectric elements 30 and 31 via the wound wire 290. This can alsosupply the drive voltage to the piezoelectric elements 30 and 31 with asimple conductive construction. When the voltage is supplied via theelastic conductive member 280 or the wire 290 as described above, thestacked structure of the vibrating plate 10 may be either a structure inwhich electrodes are arranged on upper and lower surfaces or a structurein which the reinforcing plates formed of conductors are formed on theupper and lower surfaces. In addition to the vibrating plate having thestacked structure of the piezoelectric elements and the reinforcingplates, the above-described elastic conductive member 280 or the wire290 can be used when the voltage is supplied to the piezoelectricelements.

B. Second Embodiment

Next, a description will be given of a piezoelectric actuator accordingto the second embodiment of the present invention. In the secondembodiment, components common to those of the first embodiment areindicated by the same reference numerals, and a description thereof willbe omitted.

As shown in FIG. 46, the piezoelectric actuator according to the secondembodiment includes a vibrating plate 310 in place of the vibratingplate 10 of the piezoelectric actuator A1 according to the firstembodiment.

As shown in FIG. 47, the vibrating plate 310 has a structure in whichpiezoelectric elements 30 and 31 are stacked on upper and lower sides ofa reinforcing plate 32 in a manner similar to the vibrating plate 10 inthe first embodiment. However, as shown in FIG. 48, the vibrating plate310 differs from the vibrating plate 10 in that electrodes 33 a, 33 b,33 c, and 33 d are arranged on the piezoelectric elements 30 and 31. Inaddition, in the vibrating plate 310, the piezoelectric element 30 (alsothe piezoelectric element 31 although it is not shown, FIG. 4 is dividedinto four regions, and the electrodes 33 a, 33 b, 33 c, and 33 d arearranged on the divided regions, respectively.

A description will be given of a conductive construction for supplyingthe drive voltage to the electrodes 33 a, 33 b, 33 c, and 33 d arrangedon the four regions of the piezoelectric element 30 with reference toFIG. 49. As shown in the figure, by switching ON/OFF of a switch(selection unit) 341, a mode for supplying the drive voltage from apower source 340 to all of the electrodes 33 a, 33 b, 33 c, and 33 d,and a mode for supplying the drive voltage from the power source 340 tothe electrodes 33 a and 33 d can be switched.

When the switch 341 is turned on, and the mode for supplying the drivevoltage to all of the electrodes 33 a, 33 b, 33 c, and 33 d is selected,the vibrating plate 310 expands and contacts in the longitudinaldirection to cause a longitudinal vibration in a manner similar to theabove-described first embodiment (hereinafter, referred to as alongitudinal vibration mode), as shown in FIG. 50(a). On the other hand,when the switch 341 is turned off, and the mode for supplying the drivevoltage only to the electrodes 33 a and 33 d is selected, thepiezoelectric elements 33 a and 33 d only in the regions to which thedrive voltage is applied expand and contract, and the vibrating plate310 causes a bending vibration in the widthwise direction (verticaldirection in the figure) within a plane to which the vibrating plate 310belongs (hereinafter, referred to as a bending vibration mode), as shownin FIG. 50(b). By switching the switch 341 in this way, the vibrationmode of the vibration plate 310 can be selected.

In the piezoelectric actuator according to the second embodiment, therotor 100 is driven using the vibrating plate 310 that can switch thetwo vibration modes as described above, and the driving direction of therotor 100 can be switched by operating the switch 341 to switch thevibration modes. When the longitudinal vibration mode is selected, aleftward driving force in the figure is provided by the longitudinalvibration of the vibrating plate 310 from the abutting part between therotor 100 and the projection 36, as shown in FIG. 51, whereby the rotor100 is rotated in a clockwise direction in the figure.

On the other hand, when the bending vibration mode is selected, anupward driving force in the figure is provided by the bending vibrationof the vibrating plate 310 from the abutting part between the rotor 100and the projection 36, as shown in FIG. 52, whereby the rotor 100 isrotated in a counterclockwise direction in the figure.

In the piezoelectric actuator according to the second embodiment, therotor 100 can be driven in a normal direction and an opposite directionby switching the switch 341. Since the driving direction is switched byswitching the vibration modes of the vibrating plate 310 as describedabove, there is no need to provide a vibrating plate for each drivingdirection, and to provide an adjustment mechanism for adjusting thepositional relationship between the vibrating plate and the rotor thatis an object to be driven. Therefore, the driving direction can beswitched between the normal direction and the opposite direction withoutcomplicating the construction and increasing the size of the device.

In the piezoelectric actuator according to the second embodiment,various modifications can be made in a manner similar to theabove-described first embodiment. For example, a cutout may be providedin the vibrating plate 310 in place of the projection 36 (see FIG. 20).In addition, the end 38 of the support member 11 may be located on atangent to the projection 36 of the vibrating plate 310 and the rotor100 so that the contact state between the projection 36 and the rotor100 is stabilized (see FIG. 31). Furthermore, a spring member may beprovided in addition to the support member 11 so that the vibratingplate 310 is urged toward the rotor 100 by the spring member (see FIG.35).

C. Third Embodiment

Next, a description will be given of a piezoelectric actuator accordingto the third embodiment of the present invention. In the thirdembodiment, components common to those of the first and secondembodiments are indicated by the same reference numerals, and adescription thereof will be omitted.

While the vibrating plate is urged toward the rotor 100 by an urgingforce of the spring member or the support member in the above-describedfirst and second embodiments, the rotor 100 is urged toward thevibrating plate in the third embodiment. A description will be given ofthis construction with reference to FIG. 53. As shown in the figure, inthis embodiment, a rotating shaft 100 j of the rotor 100 is supported onone end of an elastic rotating member 550, and the rotating shaft 100 jis rotatable around a rotating shaft 550 a of the elastic rotatingmember 550. The elastic rotating member 550 is composed of a rotatingportion 550 b of which one end supports the rotating shaft 100 j and theother end is rotationally supported around the rotating shaft 550 a, anda spring portion 550 c extending from the side of the rotating shaft 550a of the rotating portion 550 b while being bent thereat. The sidesurface of the spring portion 550 c is supported by a raised pin 551,whereby the rotating portion 550 b is urged to rotate in a clockwisedirection in the figure. That is, the rotating shaft 100 j of the rotor100 is urged rightward in the figure.

On the other hand, the vibrating plate 10 is, unlike the firstembodiment, supported by support members 552 formed of a rigid body atwidthwise both ends thereof. The support members 552 support thevibrating plate 10 at the position of a node of vibration when thevibrating plate 10 vibrates, and the position of the vibrating plate 10and mounting portions 553 of the support members 552 are fixed. Byfixing the vibrating plate at the position of the node of vibration, thevibration of the vibrating plate 10 can be stabilized. Even if thevibrating plate 10 is fixedly supported, since the rotor 100 is urgedtoward the vibrating plate 10, sufficient friction is produced betweenthe outer peripheral surface of the rotor 100 and the projection 36,whereby the driving force can be transmitted therebetween with higherefficiency.

When the piezoelectric actuator has a gear mechanism and the like forincreasing or decreasing a speed, such as a first gear 555 that iscoaxial with the rotor 100, i.e., rotated together with the rotor 100using the rotating shaft 100 j as a rotating shaft, and a second gear556 meshed with the first gear 555, it is preferable that components bearranged so that the rotating shaft 550 a of the elastic rotating member550, the rotating shaft 100 j, and a rotating shaft 556 a of the secondgear 556 are arranged substantially on the straight line L, as shown inthe figure, and that the vibrating plate 10 is arranged so that theprojection 36 is located in the direction perpendicular to the line Lfrom the rotating shaft 100 j of the rotor 100. This is because, byarranging the components in this way, even if the elastic rotatingmember 550 is rotated due to variations during mounting, variations insize, and the wear of the contact part, the contact angle between therotor 100 and the projection 36 does not change very much, whereby agood contact state can be maintained. In addition, when the first gear555 is rotated, the positional relationship between the first gear 555and the second gear 556 does not change very much, whereby the drivingforce can be stably transmitted.

In the above-described construction, when a load applied to the secondgear 556 is increased, that is, when a force which tends to rotate thesecond gear 556 in a direction opposite to a driving direction that is acounterclockwise direction in the figure is increased, a force whichtends to rotate the first gear 555 and the rotor 100 in a clockwisedirection is also increased. That is, a force received by the first gear555 on the right side in the figure at a meshed portion with the secondgear 556 is increased. In accordance with the increase, a force whichtends to rotate the elastic rotating member 550 for supporting therotating shaft 100 j in a clockwise direction in the figure isincreased, whereby the force of the outer peripheral surface of therotor 100 pressing against the projection 36 is increased. When theforce of the outer peripheral surface of the rotor 100 pressing againstthe projection 36 is increased in this way, the friction between therotor 100 and the projection 36 is increased, and a torque that can betransmitted from the vibrating plate 10 to the rotor 100 is increased.In this way, in this piezoelectric actuator, the torque can be increasedas the load increases. Conversely, when the load is decreased, thefriction between the outer peripheral surface of the rotor 100 and theprojection 36 is decreased, but the decrease in the friction makes itpossible to drive the rotor 100 with a low power. Therefore, in thepiezoelectric actuator according to the third embodiment, the maximumtorque can be improved although it can be operated with a low powerconsumption during the low-loaded state.

While the rotating shaft 100 j of the rotor 100 is movable, and theelastic rotating member 550 urges the rotor 100 toward the vibratingplate 100 in the third embodiment, the rotor 100 may be formed of anelastic body so that the outer peripheral surface of the rotor 100 ispressed toward the vibrating plate 10 by an elastic force of the rotor100, as shown in FIG. 54. In this case, if the position of the rotatingshaft 100 j of the rotor 100 is fixed to a position such that the rotor100 that does not receive the external force, that is, the rotor 100that is not elastically deformed, is arranged where the outer peripheralsurface shown by the two-dot chain line in the figure crosses theprojection 36 each other, the outer peripheral surface of the rotor 100and the projection 36 are pressed into contact with each other by theelastic force of the rotor 100 which tends to return to the formershape, whereby sufficient friction is produced between the outerperipheral surface of the rotor 100 and the projection 36, and thedriving force can be efficiently transmitted. As such an elastic rotor100, a metallic member can be uses as long as it has hollow sections, asshown in the figure.

In addition to the above-described vibrating plate 10, vibrating platesin various forms may be used in the third embodiment in a manner similarto the first embodiment, and a vibrating plate that is able to selectbetween the longitudinal vibration mode and the bending vibration modelike the vibrating plate 310 shown in the second embodiment may be used.

D. Fourth Embodiment

Next, a description will be given of a piezoelectric actuator accordingto the fourth embodiment of the present invention. In the fourthembodiment, components common to those of the first to third embodimentsare indicated by the same reference numerals, and a description thereofwill be omitted.

As shown in FIGS. 55, and 56 the piezoelectric actuator according to thefourth embodiment has a structure in which one end of the vibratingplate 10 is overlapped on the surface of a disk-like rotor 100. As shownin FIG. 56, the vibrating plate 10 is inclined with respect to the planeof the rotor 100, and a projection 700 projected from the vibratingplate 10 toward the plane of the rotor 100 abuts against the plane ofthe rotor 100 from an oblique direction.

In this construction, when a voltage is applied to a piezoelectricelement of the vibrating plate 10 from a driving circuit (not shown),the vibrating plate 10 causes a longitudinal vibration in the directionshown by the arrow in the figure. When the vibrating plate 10 vibratesin such a manner as to extend toward the center of the rotor 100 duringthe longitudinal vibration, the one end 700 is displaced while it is incontact with the plane of the rotor 100, whereby the rotor 100 isrotationally driven in a clockwise direction shown by the arrow in FIG.55.

The vibrating plate 10 may be provided not only on the front surface ofthe rotor 100 but also on the back surface of the rotor 100. Inaddition, as shown in FIG. 57, a projection 710 projected downward fromthe projection 700 may be provided instead of inclining the vibratingplate 10 with respect to the rotor 100, and the projection 710 may bebrought into abutment with the plane of the rotor 100.

In addition to the above-described vibrating plate 10, vibrating platesin various forms may be used in the fourth embodiment in a mannersimilar to the first embodiment.

Furthermore, a vibrating plate that is able to select the longitudinalvibration mode and the bending vibration mode may be used so as toswitch the driving direction of an object to be driven. In this case, avibrating plate 580, which vibrates in a manner similar to the abovevibrating plate to drive the rotor 100 in the longitudinal vibrationmode, and causes a bending vibration in an out-of-plane direction shownin FIG. 58 in the bending vibration mode may be provided, and in thebending vibration mode, the rotor 100 may be driven rightward in thefigure that is a direction opposite to the direction in the longitudinalvibration mode.

When switching the longitudinal vibration mode and the bending vibrationmode in this way, a driving circuit shown in FIG. 59 may be constructed.When a switch 581 are switched between the longitudinal vibration modeand the bending vibration mode as shown in the figure, two stackedpiezoelectric elements 30 and 31 vibrate in the same phase in thelongitudinal vibration mode, whereby the vibrating plate can be allowedto cause a longitudinal vibration in an in-plane direction, and thepiezoelectric elements 30 and 31 vibrate in the opposite phase in thebending vibration mode, whereby the vibrating plate can be allowed tocause a bending vibration in an out-of-plane direction. The arrows inthe figure indicate a direction of polarization.

E. Modifications

While the piezoelectric actuator rotationally drives the disk-like rotorin the above-described various embodiments, an object to be driven isnot limited thereto. For example, the above-described vibrating plate 10may be brought into abutment with a driving member 660 that issubstantially shaped like a rectangular parallelepiped so as to drivethe member 660 shaped like a rectangular parallelepiped in thelongitudinal direction thereof, as show in FIG. 60

The piezoelectric actuator according to the above-described variousembodiments can be used by being incorporated in a portable device otherthan a timepiece that is driven by a battery, in addition to beingincorporated in the above-described calendar display mechanism of atimepiece.

While a plate-like member is used as the reinforcing plate 32 in theabove-described various embodiments, a metallic film formed bysputtering and the like may be used as a reinforcing portion stacked onthe piezoelectric element, and any method may be adopted to form themetallic film.

1. A piezoelectric actuator for moving a target object, comprising: abase frame; and a motion stimulator including: a vibrating plateincluding piezoelectric material and reinforcing support materialstacked upon each other, said reinforcing support material beingeffective for restricting unloaded vibratory movement of said vibratingplate, wherein said vibrating plate is not in contact with said targetobject, to a longitudinal direction substantially parallel to thesurface plane of said vibrating plate; and a support arm having a firstend fixed to said base frame and a second end fixed to a side of saidvibrating plate at a point within the longitudinal extremes of saidvibrating plate, said support arm providing an elastic force for urginga longitudinal end of said vibrating plate to abut against said targetobject such that said longitudinal direction is aligned toward saidtarget object; wherein, when said piezoelectric material vibrates, saidvibrating plate is caused to vibrate and drive said target object.
 2. Apiezoelectric actuator as claimed in claim 1, wherein said support armsupports said vibrating plate at a point off of the vibrating plate'scenter of gravity toward said target object.
 3. A piezoelectric actuatoras claimed in claim 2, wherein the vibrating plate is supported in sucha manner that as the vibration of said piezoelectric material forcessaid vibrating plate against said target object, said target objectapplies a reactionary deflective force on said vibrating plate along adirection intercepting said longitudinal direction, said deflectiveforce causing lateral flexing in said vibrating plate that increases thecontact duration during which said vibrating plate applies a drivingforce onto said target object due to the vibrating of said piezoelectricmaterial.
 4. A piezoelectric actuator as claimed in claim 3, whereinsaid deflective force is perpendicular to said longitudinal directionand the flexing motion of said vibrating plate has a longitudinal motioncomponent due to the longitudinal vibratory force of said piezoelectricmaterial and a lateral motion component due to said deflective force,said longitudinal motion component having a first resonance frequencyand said lateral motion component having a second resonance frequency atleast equal to said first resonance frequency.
 5. A piezoelectricactuator as claimed in claim 4, wherein said second resonance frequencyis higher than said first resonance frequency, and the frequency of theactivation signal applied to said piezoelectric material is intermediatesaid first and second resonance frequencies.
 6. A piezoelectric actuatoras claimed in claim 3, wherein the shape of said vibrating plate isselected such that the flexing motion of said vibrating plate, caused bysaid reactionary deflective force in combination with the vibratingforce of said piezoelectric material, has a wavelength shorter than thelength of said vibrating plate along its longitudinal side, whereby awave node is created within said vibrating plate during its vibratorymotion, and the point at which said second end of said support arm isfixed to said vibrating plate coincides with said wave node.
 7. Apiezoelectric actuator as claimed in claim 1, wherein the end of thevibrating plate abutting against said target object has a roundedprojection, and the projection abuts against said target object.
 8. Apiezoelectric actuator as claimed in claim 1, wherein the longitudinalvibration in which the vibrating plate expands and contracts in thelongitudinal direction is generated by the vibration of thepiezoelectric element, and a bending vibration in which the vibratingplate vibrates in the widthwise direction perpendicular to thelongitudinal direction is generated by a reaction force received by thevibrating plate from said target object due to the longitudinalvibration.
 9. A piezoelectric actuator as claimed in claim 8, whereinthe resonance frequencies of the longitudinal vibration and the bendingvibration generated in the vibrating plate substantially coincide witheach other.
 10. A piezoelectric actuator as claimed in claim 8, whereinthe resonance frequency of the bending vibration generated in thevibrating plate is higher than the resonance frequency of thelongitudinal vibration generated in the vibrating plate.
 11. Apiezoelectric actuator as claimed in claim 10, wherein the excitingfrequency for driving the piezoelectric element is a frequency betweenthe resonance frequency of the longitudinal vibration generated in thevibrating plate and the resonance frequency of the bending vibrationgenerated in the vibrating plate.
 12. A piezoelectric actuator asclaimed in claim 1, wherein the wavelength of the vibratory motion ofsaid vibrating plate is selected to be shorter than the length of saidvibrating plate along its longitudinal side, whereby a wave node iscreated within said vibrating plate during its vibratory motion, and thepoint at which said second end of said support arm is fixed to saidvibrating plate coincides with said wave node.
 13. A piezoelectricactuator as claimed in claim 1, wherein said reinforcing supportmaterial is thinner than said piezoelectric material.
 14. Apiezoelectric actuator as claimed in claim 1, wherein said supportmaterial includes at least first and second support sheets, and saidpiezoelectric material is between said first and second support sheets,said first support sheet being an electrode for applying an excitationsignal to said piezoelectric material.
 15. A piezoelectric actuator asclaimed in claim 14, wherein said second support sheet is an electrode,and wherein power is supplied to said piezoelectric material via saidfirst and second support sheets stacked on the upper and the lower sidesof said piezoelectric material.
 16. A piezoelectric actuator as claimedin claim 14, wherein said support arm is a conductor fixed to said firstsupport sheet, and wherein power is supplied to said piezoelectricmaterial via said support arm.
 17. A piezoelectric actuator as claimedin claim 14, wherein; said support material includes at least onereinforcing, inter-layer sheet not in contact with either of said firstand second support sheets; and said piezoelectric material includes aplurality of piezoelectric sheets separated by a corresponding one ofsaid interlayer sheets.
 18. A piezoelectric actuator as claimed in claim17, wherein said second support sheet is a second electrode, and thethickness of said first and second supports sheets is smaller than saidinter-layer sheet.
 19. A piezoelectric actuator as claimed in claim 18,wherein said first support sheet is at least 0.5 μm thick.
 20. Apiezoelectric actuator as claimed in claim 17, wherein adjacentpiezoelectric sheets are polarized in opposite directions.
 21. Apiezoelectric actuator as claimed in claim 17, wherein adjacentpiezoelectric sheets are polarized in the same direction.
 22. A timepiece comprising: a piezoelectric actuator as claimed in claim 1; andwherein said target object is a ring-shaped calendar display wheelrotationally driven by the piezoelectric actuator.
 23. A portable devicecomprising: a piezoelectric actuator as claimed in claim 1; and abattery for supplying power to the piezoelectric actuator.
 24. Apiezoelectric actuator as claimed in claim 1, wherein said point, withinthe longitudinal extremes of said vibrating plate, to which said secondend of said support arm is fixed, is located within the proximity of thecenter of the lateral length of said vibrating plate and offset towardsaid target object.
 25. A piezoelectric actuator as claimed in claim 1,wherein said support arm is a conductor and applies an excitation signalto said vibrating plate.
 26. A piezoelectric actuator comprising: a baseframe; a rotor having an outer side-peripheral surface, and rotationallysupported on said base frame; and a motion stimulator including: avibrating plate in which a piezoelectric element and a reinforcing sheetare stacked, said reinforcing sheet being effective for restrictingunloaded vibratory movement of said vibrating plate, wherein saidvibrating plate is not in contact with said rotor, to a longitudinaldirection substantially parallel to the surface plane of said vibratingplate; and a support arm having a first end fixed to said base frame anda second end fixed to a side of said vibrating plate at a point withinthe longitudinal extremes of said vibrating plate, said support armproviding an elastic force for urging a longitudinal end of saidvibrating plate to abut against said side-peripheral surface of saidrotor; wherein, when said piezoelectric element vibrates, said vibratingplate is caused to vibrate in said longitudinal direction and drive saidrotor in one direction in accordance with the displacement of saidvibrating plate.
 27. A piezoelectric actuator as claimed in claim 26,wherein said support arm supports said vibrating plate at a point off ofthe vibrating plate's center of gravity toward said rotor.
 28. Apiezoelectric actuator as claimed in claim 27, wherein the vibratingplate is supported in such a manner that as the vibration of saidpiezoelectric material forces said vibrating plate against saidside-peripheral surface of said rotor, said side-peripheral surfaceapplies a reactionary deflective force on said vibrating plate along adirection intercepting said longitudinal direction, said deflectiveforce causing lateral flexing in said vibrating plate that increases thecontact duration during which said vibrating plate applies a drivingforce onto said rotor due to the vibrating of said piezoelectricmaterial.
 29. A piezoelectric actuator as claimed in claim 28, whereinsaid deflective force is perpendicular to said longitudinal directionand the flexing motion of said vibrating plate has a longitudinal motioncomponent due to the longitudinal vibratory force of said piezoelectricmaterial and a lateral motion component due to said deflective force,said longitudinal motion component having a first resonance frequencyand said lateral motion component having a second resonance frequency atleast equal to said first resonance frequency.
 30. A piezoelectricactuator as claimed in claim 29, wherein the longitudinal end of saidvibrating plate abutting against said rotor has a rounded projection,and it is this projection that abuts against said side-peripheralsurface of said rotor; and wherein said second resonance frequency ishigher than said first resonance frequency, and the frequency of theactivation signal applied to said piezoelectric material is intermediatesaid first and second resonance frequencies.
 31. A piezoelectricactuator as claimed in claim 27, wherein the end of said vibrating plateabutting against said rotor has no protrusion and has a curved surface.32. A piezoelectric actuator as claimed in claim 31, wherein the end ofsaid vibrating plate abutting against said rotor is curved as viewedfrom above the top surface plane of said vibrating plate.
 33. Apiezoelectric actuator as claimed in claim 31, wherein the end of saidvibrating plate abutting against said rotor is curved as viewed from theside edge of the vibrating plate.
 34. A piezoelectric actuator asclaimed in claim 33, wherein the base frame has a single member forsupporting both the rotor and the vibrating plate.
 35. A piezoelectricactuator as claimed in claim 27, wherein the longitudinal vibration isgenerated by the longitudinal expanding and contracting of saidvibrating plate due to the excitation of said piezoelectric element, anda bending vibration in which the vibrating plate vibrates in a widthwisedirection perpendicular to the longitudinal direction is generated by areaction force received by the vibrating plate from the rotor due to thelongitudinal vibration.
 36. A piezoelectric actuator as claimed in claim35, wherein the resonance frequency of the bending vibration generatedin the vibrating plate is higher than the resonance frequency of thelongitudinal vibration generated in the vibrating plate.
 37. Apiezoelectric actuator as claimed in claim 36, wherein the excitingfrequency for driving the piezoelectric element is a frequency betweenthe resonance frequency of the longitudinal vibration generated in thevibrating plate and the resonance frequency of the bending vibrationgenerated in the vibrating plate.
 38. A piezoelectric actuator asclaimed in claim 27, wherein the wavelength of the vibratory motion ofsaid vibrating plate is selected to be shorter than the length of saidvibrating plate along its longitudinal side, whereby a wave node iscreated within said vibrating plate during its vibratory motion, and thepoint at which said second end of said support arm is fixed to saidvibrating plate coincides with said wave node.
 39. A piezoelectricactuator as claimed in claim 27, wherein a longitudinal vibration inwhich the vibrating plate expands and contracts in the longitudinaldirection is generated by the vibration of the piezoelectric element,and the end of the vibrating plate abutting against the rotor iselastically deformed in the widthwise direction perpendicular to thelongitudinal direction by a reaction force received by the vibratingplate from the rotor due to the longitudinal vibration.
 40. Apiezoelectric actuator as claimed in claim 26, wherein a concave grooveis formed in said side-peripheral surface of said rotor.
 41. Apiezoelectric actuator for moving a target object, comprising: a framingmeans, and a motion stimulating means including: a vibrating meansincluding a piezoelectric material and a reinforcing support materialstacked upon each other, said reinforcing support material beingeffective for restricting unloaded vibratory movement of said vibratingmeans, wherein said vibrating means is not in contact with said targetobject, to a longitudinal direction substantially parallel to a qsurface plane of said vibrating means; and a supporting means having afirst end fixed to said framing meaning and a second end fixed to a sideof said vibrating means at a point within the longitudinal extremes ofsaid vibrating means, said supporting means providing elastic force forurging a longitudinal end of said vibrating means to abut against saidtarget object such that said longitudinal direction is aligned towardsaid target object; wherein, when said piezoelectric material vibrates,said vibrating means is caused to vibrate and drive said target object.42. A piezoeletric actuator comprising: a framing means; a rotor havingan outer side-peripheral surface, and rotationally supported on saidframing means; and a motion stimulating means including: a vibratingmeans in which a piezoelectric element and a reinforcing sheet arestacked, said reinforcing sheet being effective for restricting unloadedvibratory movement of said vibrating means, wherein said vibrating meansis not contact with said rotor, to a longitudinal directionsubstantially parallel to a surface plane of said vibrating means, and asupporting means having a first end fixed to said framing means and asecond end fixed to a side of said vibrating means at a point within thelongitudinal extremes of said vibrating means, said support armproviding elastic force for urging a longitudinal end of said vibratingmeans to abut against said side-peripheral surface of said rotor;wherein, when said piezoelectric element vibrates, said vibrating meansis caused to vibrate in said longitudinal direction and drive saidrotor.